The goal of the proposed research is to gain insight into the function(s) of a recently identified growth factor encoded by the murine Steel (S1) locus. Numerous semidominant mutations exist at this locus that cause deficiencies in melanocytes, germ cells and hematopoietic cells indicating a requirement for the S1 gene product in the development or function of these cells. One goal of the proposed research is to further characterize the structure and expression of the wild type S1 locus. This will provide information and reagents required to study specific aspects of S1 function (s) in mutant mice. Other goals of the proposed work will focus on the role(s) of the S1 gene product in germ cell development. A particularly interesting phenotype of some S1 mutants is a sex-specific effect on fertility. A combination of molecular, embryological and genetic techniques will be used to identify the nature of the mutation and the developmental defects in two viable S1 alleles that cause female sterility but don't affect male fertility. Another postdoctoral fellow in this laboratory is characterizing a S1 mutation that affects only male fertility. Because the mouse gene is very closely related to its human homologue, the information gained may be applicable to some human syndromes and diseases.